#include <iostream>
#include <queue>
#include <vector>
using namespace std;

int n;
int d[10005];
vector<int> v[10005];
int cur, ans[10005];

void topusort()
{
	queue<int> q;
	for (int i = 1; i <= n; i++)
		if (d[i] == 0)
			q.push(i);
	while (!q.empty())
	{
		int f = q.front();
		ans[++cur] = f;
		q.pop();
		for (int i = 0; i<v[f].size(); i++)
		{
			int t = v[f][i];
			d[t]--;
			if (d[t] == 0)
				q.push(t);
		}
	}
}

int main()
{
	scanf("%d", &n);
	for (int i = 1; i <= n; i++)
	{
		int x, y;
		cin >> x >> y;
		d[y]++;
		v[x].push_back(y);
	}
	topusort();
	if (cur != n) 
		printf("图中有环，无法进行拓扑排序！！！\n");
	else
	{
		printf("拓扑排序后的序列：");
		for (int i = 1; i <= cur; i++)
			printf("%d ", ans[i]);
		puts("");
	}
	return 0;
}

